Art of cracking hydrocarbons



Nov. 18, 1930. J. E. BELLE-r AL 1,782,055

ART oF GRACKING HYDROCARBONS Filed Nov. l2, 1924 3 Sheets-Sheet 1INVENTOR 5 Jo f BE//a/:dfa/Ward iff/i002 BY l A4/aw ATTORNEYS Nov. 1s,1930.

l.l.'l:. BELL ET AL 1,782,056

ART OF CRACKING HYDROCARBONS IPE/70x TUWER TAR 4- 'l INVENTORS gulli,Quan/M MM 'ATTORNEY 3 Sheets-Sheet 3 Nov. 18, 1930. J. E. BELL l-:T AL

ART 0F QRACKING HYDRocARBoNs Filed Nov. 12, 1924 Patented Nov. 18, 1930UNI-TED s'rA'ras `PATENT OFFICE JOHN E 1sE1.LOr` nnOOxLYN, AND EDWARD W.rsou, OE LOCUs'r VALLEY, NEW YORK, yAssiofNoas To sINCLAIn'nErININeCOMPANY, or CHICAGO, ILLINOIs, A CORPORA- TION OF IAINE ART or CnA'cxINGHYDBOCARBONS ppliotion filed November 12, 1924. Serial No. 749,402.

This invention relates to improvements in cracking heavier hydrocarbonoils, such as gas oil, for the production of lighter hydrocarbon oils,such as gasoline or pressure distillate, bydistillation under pressure.This application is in part a continuation of our copending applicationSerial No. 437,662,-

iled January 17, 1921, which has issued as PatentpNo. 1,547 ,993.

In' cracking hydrocarbonl oils by distillation under pressure, the Oilis heated to a cracking temperature under pressure and the heavier oil,or a portion thereof, is broken down or cracked with the formation oflighter oils which are vapori'zed and driven off. The cracking operationtakes place gradually and progressively, part of the crackedconstituents escapin as pressure distillate and part of the heaviercracked constituents remaining and mixing with the charge of oil in thepressure still. A small amount of asphaltic, or pitch-likevconstituents, or heavy tar is also formed by the cracking operation.This tar remains in the charge and gradually accumulates due to thevaporization of cracked constituents and to the progressive formation oftar constituents. This tar accumulatingin the oil in the still tends todeposit on the eating surfaces of the still and 1n contact therewithtends to form a carbonaceous deposit thereon closely adhering thereto.Such carbonaceous materials ,and the heavy tar accumulating in the stillcharge are poor conductors Aof heat and when deposited on the heatingsurfaces of the vstill which `are externally exposed to heating gasesinterfere wlth heat transfer and insulate the wall from the' protectionafforded -by the Oil so that the walls of the still are apt to becomeOverheated the temperature of the metal of the heat transferring wallincreasing over that of the oil to an extent dependent upon thethickness of the deposit and the amount of heat externally delivered tothe Wall from the heating gases.' As a conseuence the pressure stillmust frequently be s iut down for cleaning or the temperature of theheating gases must be reduced below that which is most efficient. Thereis also considerable danger involved due to possible bursting of theheat transferring walls at overheated points. The heating surfaces overwhich heatin gases are first circulated are exposed to the ighesttemperature of the heating gases and absorb the greatest amount of heat,and vthese surfaces are most apt to suffer. Heating surfaces immediatelyadjacent the furnace em loyedv to heat the pressure still may also asorb large amount of heat by direct radiation from the furnace.

'According to the present invention, the vaors from the crackingoperation vare sub- ]ected to a reiuxing operation indirect contact withfresh oil and the reflux and admixed fresh oil are employed to\protectthe heating surfaces of the pressure still while at the same time thereflux and admixed fresh oil are subjectedy to advantageous crackingconditions. All of the refiuxed constituents have been vaporized fromthe charge of oil in the still and are substantially free from tarconstituents, and the fresh oil and admixed refiuxed constituents; whenadmixed with the still charge, or a part thereof, assist vin reducingthe concentration of tar constituents and in maintaining theconcentration ofl tar constituents below saturation therein. A Accordingto the present invention, the relflux and admixed -fresh oil are firstbrought .intoheat exchanging relation with the heatmg gases at theirighest tem erature before they are passed over other eating surfaces ofthe pressure still, and, as the light cracked constituents are va orizedand the Oil loses its content of crac able hydrocarbons and as theconcentration of tar constituents increases, the oil isbrought into heatexchan 'ng relation with heatinof gases which ave been tempered and reuced in temperature by heat exchange with the reflux and. admixed freshoil by passing the Oil of increased tar content over more remote'heatingsurfaces of the pressure still. The heatingv gases while at highesttemperature are thus passed over heatin surfaces which are in contactwith oil relatively free of tar constituents, or in which theconcentration of tar is least, and as the tar concentration increasesthe oil is passed over heating surfaces in contact with progressivelytempered and cooler heating gases. The lighter crack-r able constituentsof the reflu'xand admixed fresh oil are also subjected to advantageouscracking condition by heat exchangewith the hottest heating. gases. Theheating surfaces of the pressure still most apt'to suffer are thusprotected by absorption of the heat transferred therethrough in heatingand cracking the oil constituentsof the reflux and admixed fresh oil andthis heat available at high temperature is advantageously employed in auseful crackin operation rather than in the further crac ing of tarconstituents while a. reduced concentration of tar constituents ismaintained in theI oil in contact with these [initial heating surfacespreventin or materially reducing the formation o carbonaceous depositsthereon. The heat available in the heating gases, the temperature ofwhich has been lowered by the heat absorbed in heating and cracking thereflux and admixed fresh oil, is then further employed to advantage incracking the oil as tar constituents accumulate therein.

In carrying out the invention, the heating surfacesf the pressure stillmay be further protected and theV heating of the pressure still chargeequalized by providing `progressively increased areas of heat transferbetween the oil and the heating gases as the tar content of the oilincreases and as the temperature of the heatingl gases decreases. Theheating eil'ect is thus equalized by increasing the area of heattransfer as the temperature of the heating gases decreases while anincreased area of heating surface is provided in contact with the oilcontaining an increased tar content where deposition is most likely tooccur. Additional fresh oil may also be passed overA the initial heatingsurfaces together with the reiux and admixed fresh oil returned from therefluxing operation. The tar content of the pressure still charge mayalso be controlled and reduced by withdrawing tar from one or moreportions of the still charge where the tar tends to accumulate.

The present invention is of s cial value and-application in connectionwith cracking operations in which directed circulation of the stillcharge is maintained over the heating surfaces of the pressure still.Circulation may be maintained by convective action, or by mechanicalforcing means such as a pum or pumps, or by the introductionof suita legases. Circulation further assists'in preventing or materially reducingthe forma'- tion of carbonaceous deposits on the heating surfaces andassists in carr 'ng tar constituents with the circulating oily.lCirculation of the oil over the heatin motes the heat transfer om theheating surface to the oil and further rotects the heating surface inthis way. irected circulawhich the re surfaces also protion may bemaintained either in the initial heating stagesor in the later heatingstagesor in both. l Th'e process of the invention may also withadvantage be carried out in a series of stages or cycles, withcirculation of the oil in each stage or cycle froma body of the oil inheat exchanging relation with the heating gases and back tothe body, andtransferring oil to successive stages as its tar content increases,circulating heating gases in heat exchanging relation with the oil inthe stages or cycles successively in the order of increasing tarcontent, and returning reflux and admixed fresh oil from. the refluxingoperation to which the vapors from the cracking operation are subjectedto the stage or cycle in which the oil is subjected to heat exchangewith the heating gases of highest temperature.

In one aspect, the process of the present invention ma be considered aprocess in ffiix and admixed fresh oil are first subjected to a more orless. intense cracking treatment and then, as tar and carbon accumulatein the oil, to a digestion treatment in which the crackingtemperature'is maintained by employing the heating gases from theinitial cracking treatment.

While the invention is of particular advantage where the same stream ofheating gases 1s employed for heating t-he oil in the successive stagesof the process as the temperature of the heating gases is progressivelyreduced, certain advantages of the invention may be obtained by emloying heating gases of separately regulate temperature in thesuccessi-.ve stages, employing hotter heating gases for initially heatinand cracking the reflux and admixed fres oil and progressively coolerheating gases for heating thel oil of progressively increasing tarcontent in the successive stages.

The process of the invention may be carried out in different types ofapparatus. The reflux and admixed fresh oil may be returned through atubular heater arranged to be heated by the heating gases as they firstleave the furnace and arranged to discharge the oil into a shell ordrum, or digestion chamber, for further treatment of the tar containingoil. The shell or digestion' chamber may be arranged to be heateddirectly by the heatinggases which have assed over the heater throughwhich the re ux and admixed fresh oil is circulated, or the oil in theshell or di- I' gestion chamber may be'heated b `bein circulated fromand back to the she l or igestion chamber throu h a .tubular heaterarranged for heat eisrcange with the heating gases from the firstheater. The successive heaters may also all be tubular in character or adivided pressure still may be arranged to maintainpa series of bodiesofthe oil in a. series of compartments with a separate heater ,connectedto each compartment with means form of apparatus adapted for carryingout the process of the invention.` The apparatus illustrated isdescribed and claimed inan application filed Jan'. 17, '1921, SerialNumber 437 ,662 andthe process of, the present invention is of specialvalue and application in connection with'pressure stills of this generalcharacter. The pr'ocess of the invention may,-

however, be carried out in other and different apparatus. v

In the accompanying drawings:

Fig. y1 represents a pressure still, in elevation and section with partsbroken away,

`adapted for carrying out the process of the invention,

Fig. 2 is a section on line 2-2 of Fig. 1 wiih a condenserdiagrammatically shown, an

. Fig. 3 is a fragmentary section on line 3-3 of Fig. 1.

The pressure stillillustratedcomprises a drum 4 and a series of tubularheating elements communicating therewith arranged `in the heating Hue ofa furnace 5. .The heating Hue comprises a series of connected verticalHues 6, 7, 8. and 9, the Hue 6 also.con. necting with the furnace 5 andthe Hue 9 4with a stack Hue 10. The Huesare arranged so that the heatinggases from the furnace are passed successively therethrough tothe stack.A draft tube 11 is arranged for withdrawing waste heating gases from apoint adjacent the exitl of the heating Hue 9 and returning them to theHue 6 fortempering the heating gases fresh from the furnace 5 in the Hue6. The draft 'tube may be .operated by a steam jet or other suitableforcing means. By re turningwaste heating gases inthis way, the heatinggases are tempered in thez first heating Hue, the volume and rate ofcirculation of the heating gases through the heating Hues isincreased,-and the available heat in the recycled gases may be furtherutilized. By-passes 12 and 13 provided with regulating dampers 14 and 15are provided for further controlling the distribution of heat in theseveral Hues.

The still drum 4 is provided internally with a seriesof partitions 16,-17 and 18 dividing the drum into a series .of compartments A, B, C andD and a corresponding series of heating elements separatelycommunicating with each of these compartments arel arranged in theheating Hues. The heating elementconnected to compartment A is arrangedin Hue 6, that is the Hue through diottest heating gases.

which the heating gases are Hrst passed, the heating element of the nextcompartment B in the next Hue 7, and so on, the heating elementconnectedto the last compartment D being arranged in -the plast heatingHue 9 through which vthe coolest heating gases are circulated. Thepartitions in thedrum do not completely shut olf the compartments fromeach other but extend a. short distance above the normal liquid leveltherein leaving a common vapor space iii-the upper part of the drum.OverHow pipes 19, 20 and 21 are arranged for progressively .transferringoil to successive compartments in the series, and these pipes-areprovided with bell caps to prevent transfer of surface scum and froth tosuccessive compartments.

' Each of the heating elements connected to the respective compartmentscomprises these" v similar groups of heating tubes.v Eachy of' thesegroups comprises an outHow header 22,.

a series of upwardly inclined .tubes y23 arranged through the heatingHue for heat exchange with the -heating ases therein, connecting headers24, anotier series of." up wardly inclined tubes25 arranged through theheating Hue,and an inHow header v26. I n order to facilitate cleaningand repair-the headers are arranged outside of the heating Hues and areformed-with'plugged hand holes in alignment with the heating tubes. Inorder to equalize 'the heating effect inthe several heaters and toprovide .an increased area of heat transfer as the tar content of thevoil increases, as will presently appear in more detail,vthe heattransferring vareapf the several heaters is progressively increased asthe temperature of the heating gases declines.- -In the apparatusillustrated, the heater connected to the first compartment A lon tocompartment V4B eight tubes, that 'connected to vcompartment C twelvetubes and that connected to the last compartment D sixteen tubes.` l

Arranged above the drum 4 .is a rcHux tower 27 adapted to receive vaporsfrom the vapor space of the drum 4 and to discharge ref-lux and admixedoil into the first compartment A connected to the heating elementarranged in heat exchanging relation with theA A connection 28 isprovided for introducing fresh oil into the upper part of the refluxtower over the baHles.

therein and vin direct contact with the vapors therein. A connection 29discharging into the iirst compartment A is providedfor the introductionof supplementary or additional fresh oil. The vapors escape from the-re-Hux tower through vaporl line 30 to a condenser -diagrammaticallyillustrated at 31.

The pressure inthestill may be reduced and controlled by a/regulatingvalve 32 arrangedV between the reflux tower and the condenser orbya-valve 33 arranged beyondthe condenser. In order to provide fordrainage, and for Withdrawal of tar during the cracking operation thelower ends of the inflow headers in each heating element are connectedto a manifold 34 having a valved outlet 35,

the outlet from the last compartment D being designated 35. 'u

The reflux tower and the still drum may, with advantage, be covered orprotected with suitable heat insulation, such as an asbestos or mineralwool jacket.

In carrying out the process of the invention in the apparatusillustrated, the` still is initially charged with oil, throughconnection 29 the oil successively overflowing into the adjacentcompartments as the preceding compartments are filled, and brought tothe cracking temperature and pressure in the usual way. The pressureemployed may differ with different charging stocks and for theproductionof different pressure distillates. With gas oil character chargingstocks for the production of gasoline character distillates, pressuresin the neighborhood of 90 to 1,25 pounds per square inch-or more may beemployed. In cracking a kerosene character charging stock to produce agasoline character distillate, considerably higher pressures maybe used,for example, pressures up to 300 pounds per square inch or more may beemployed.

After the still charge is broughtto the cracking temperature andpressure, the cracked vapors rise from the several compartments and passupwardly through the reflux tower27, and the introduction of fresh oilthrough connection 28 is be n. In the reflux tower the fresh oil isintimately contacted with the vapors from the still, refluxing theheavier vapors and preheating the fresh oil, and the reflux and admixedfresh oil are returned to compartment A. As the reflux and admixed freshoil are introduced into compartment A, oil from thisfirst compartmentwhich has been deprived of a part of its Vcrackable constituents andcontains some tarconstituents overflows into the second compartment Bwhere it is further cracked and a further part of its components are,

vaporized. In the same Way oil'is trans#l ferred from compartment B tocompartment C and from compartment C to compartment D asthe crackedconstituents are vaporized and as the tar accumulates, the oil in thesuccessive compartments containing less and less of the original oilconstituents and more and more heavy tarry constituents. t

Tar may also be withdrawn from one or more of the successivecompartments," and.

with particular advantage from the last compartment D through connection35. The introduction of fresh oil into the reflux tower is controlled toregulate the refluxing operation. Where no tar, or only a relativelysmall amount of tar is Withdrawn, the

amount of fresh oil introduced intothe reflux tower may correspondapproximately to the amount of distillate taken off or may be somewhatin excess of this amount. Where larger amounts of tar are withdrawn, thestill charge is maintained by the introduction of an increased amount offresh oil, and

that in the second compartment B to a somewhat lower temperature, and soon. The heat absorbed by the oil in the first compartment A is employedto crack the oil constituents of the reflux and admixed fresh oil andthis oil is circulated over the heating surfaces protecting them againstthe highest temperature of the heating gases, and as the tar content ofthe oil increases it is transferred to successive compartments where itis Subjected to heat exchange with heating gases of progressively lowertemperature. At the same time the heating effect in the successivecompartments is equalized by the progressively increased area of heattransfer provided, and the difliculties and dangers incident to theformation of carbonaceous deposits are materially reduced due both tothe decreased temperature of the heating gases and the increased area ofheat transfer and consequent reduction in the rate of heat transfer perunit of area. In all of the heating elements the absorption of heatbythe circulating oil protects the heating surfaces, particularly in thefirst where the heating element is exposed to the hottest heating gasesand where the circulating oil contains the reflux and admixed fresh oiland the least content of tar. i

y It will thus be seen that .the present in` 'vention provides animproved method of cracking hydrocarbon oils by distillation underpressure in externally heated pressure stills in which fresh oil issupplied to the cracking operation and in which the, fresh oil 'is firstemployed to promote and control a refluxing operation to which thevapors from the pressuregstill are subjected and then, in admixture withthe reflux, to-protect the heating surfaces of the pressure stillsubjected to heat `exchange with the hottest .heating gases while thelighter-crackable heating pors from said .conv

tillate,

the'heatin gases or otherwiser- Another portant a vantage of theinvention is that 1t enablesan improved applicationbfithe,

gases to the crackingloperation sothat both the eiiciency and t ecapacity of the pressure still may be increased.l

Weclaim: L'An improved method of cracking hydrocarbonfoils, whichcomprises heating' the oil to a cracking temperature under pressure lina series o stages.- and circulating the oil to successive stages Vas thetar content of the oil increases, circulating heating gases in heatexchanging vrelation successively with the oilin vthe stages in theorder in which the oil ,is-circulated there-v through, maintainingprogressively 'increas-v ing areas of heat-transfer betweenfthe heatinggases and the oil in the successive stages in the same order,`.'subjecting the vapors from the cracking operation` to a refluxing jt=fwith1j fresh oil,

operation in -direct contac and returning the reiiux a oil to the 4irststagelin d inxed fresh #new mcentration is least.'

2. /A process for-crac khydrocarbons comprising passing the oilthronghf'a heating coil wherein it is raisedftojaccnversionitemperature, l discharging "th enlarged conversion champhlegmation-and co unvaporized oil from-Sal zone than thatin.whichiis'aidf heating coil;

version temperature, in discharging the heated oil into anV enlargedconversion `chanu` ber, in passing the vapors issuing roxnsaid-.'converslon chamber to a dephlegmatonrin Vreturning refiux condensatefrom. the de-v phlegmator to said heating coil, inl condensmater `andina-collecting .the resulting disin circulating the unvaporized oil fromsaid conversion chamber through an independent heating element whereinit is subjected to a lower tempjraturethan the oil Ein said coil and bactc 4the conversion chamber', Y and in .maintainingfa superatmosphe'ricpressure on the oil undergoing conversion.

4. A process for cranking hydrocarbons comprising passing the oilthrough a heating A coil wherein it is raised to a conversiontemperature, discharging the heated voil into an enlarged conversionchamber, taking off vars from said conversion chamber and reuxing thevapors in heat exchanging relation with resh oil', circulatingunvaporized oil from said conversion chamber through ducing fresh oil tothe deph cracking hydrocarbon oil,

that inw ch said heating coil 1s positioned and 'back to the conversionchamber, and supplying the fresh oil from the refluxing zonetotheheatingcoil.- A

5. A process of cracking h drocarbon oil consisting in passin the oil trough aheatlng coil wherein it 1s subjected to a conversion temperature,in discharging the heated oil into an enlarged conversion chamber, inpassin the vapors issuinl fromsaid conversionl c amber to a dep egmator,in introcontact with'thevapors therein, 1n returning ref iux condensateand admixed fresh oil from the dephlegmator to said heating coil, incondensing the vapors issuln from the dephlegmator and in collecting t eresulting distillate, in circulating the unvaporized oil from saidconversion chamber throu h an indeendentl heating element wheremit is'suh-l jected to `a lower temperature than the oil' 1n said coil and backto the conversion chamber, and in maintalning a superatmospheric-"pressure onthe oil undergoing conversion.

6'. A n improved methodof cracking hydro` carbon oils, which comprisesycirculatin the oil in each of a series of cycles from a ed of Vtheoilin heat -exchanging relation wit heating gases' and back tothe' body,transf erringi the oil to successive-c cles as vthe ta content of theoil increases, eating the oil to a cracking temperature under pressureby ber through a cooler portion of the heating -circulating'heatinggases in heat exchanging l .relation successively with the oilin thecycles is positioned and back to. said 1conversion inthe order ofincreasing tar content, maintaining progressively increasing areas ofheat transfer between the heating gases and the oil in the successivecycles in the same order, subjecting the vapors from the crackingoperation to a reiuxing operation, and returning the reflux to the firstcycle in which the tar concentration is least. Y

:` 7. A process of cracking hydrocarbon oil, consisting in passing theoil through a-heating coil wherein it is subjected to a converfsion itemperature, in discharging the heated voil anto an enlarged converslonchamber, in `passing the vapors issuing from said conversion chamber toa de phlegmator, in returning reflux condensate from the dephle ator tosaid heatingcoil, in condensing t e vapors issuing from the dephlemator` and in jcollecting 4the resulting disti late, in circulating theunvapxorized o1l from said conversion chamber t rough an independentheating element wherein v1t is subjected to a lower temperature than'theoil in said coil and back to the conversion chamber, in preventingthereturn of unvaporized oil which has passed through said independentheating element to said heating coil, and in maintainmg'asuperatmospheric pressuregon the oil undergoing conversion.

8. A process of cracking hydrocarbon oil,

egmator in direct consisting in passing the oil through a heating coilwherein it is subjected to a conversion temperature, in discharging theheated' oil into an enlarged conversion chamber, in passing the vaporsissuing from said conversion chamber to a dephlegmator, in returningrefiux condensate from the dephlegmator together with additional freshoil to said heating coil, in condensing the vapors issuing from thedephlegmator and in co1- lecting the resulting distillate, incirculating the unvaporized oil from said conversion chamber through anindependent heating element wherein 1t is subjected to a lowertelnperature than the oil in said coil and back to the conversionchamber, in preventing the return of unvaporized oil which has passedthrough said independent heating element to said heating coil, and inmaintaining a superatmospheric pressure on the oil undergoingconversion.

In testimony whereof we ax our signatures.

JOHN E. BELL. EDWARD W. ISOM.

